1. Field of the Invention
This invention relates to a radio telephone system and a method for controlling the radio telephone system comprising a radio telephone set utilizing a rechargeable battery as its electric source, and a base unit connected to the radio telephone set through a radio channel and through which speech signals are transmitted between the radio telephone set and a wired telephone line, and more particularly, a radio telephone system and its controlling method capable of prohibiting a continuous transmission state caused by the failure in the operation of a speech channel termination switch while the battery of the radio telephone set is being charged.
2. Description of the Prior Art
As is well known in the art, a prior art radio telephone system is constituted by a base unit connected to a wired telephone line, and a radio telephone set controlled by the base unit for exchanging speech signals between the radio telephone set and the wired telephone line. When an origination switch in the radio telephone set is operated, a control circuit controls a transmitter and a receiver to establish a radio speech channel between the radio telephone set and the base unit, thus permitting speech. When the speech is terminated, a termination switch is closed for terminating the speech channel.
In an ordinary telephone set, the origination and the termination of the speech channel are effected by on-hook and off-hook operations of a handset of the telephone set, but in some type of the radio telephone systems, the origination and the termination of the speech channel are controlled by independent switches.
In such a system, if the speech channel termination switch fails to be operated when the speech has terminated, the speech channel between the base unit and the radio telephone set, and further between the base unit and the wired telephone line will remain in the speech state, thus prohibiting the channel from being used for other speeches.
Especially, in a system constructed such that the radio telephone set is mounted on and connected to the base unit when not in use so as to charge the battery in the radio telephone set and it is dismounted when in use, since electricity in the electric source is not consumed during the charging, the speech state will be maintained until the troubles is noticed and the speech channel termination switch is operated.
For this reason, a display device or a warning device has been used for informing the fact that the speech state is maintained or a timer is provided for automatically terminating the speech channel when the speech state is maintained beyond a predetermined period.
In the system in which whether the telephone system is in the speech state or not is informed by a display device, the display is likely to be mistaken as a display of other display devices so that there is a defect that the speech channel termination switch cannot be operated correctly.
Where the speech channel is forcibly terminated, there will be a case in which the speech channel is unfavorably terminated during actual talking.